Details

Hot air engine is a catch-all term for any heat engine which uses the expansion and contraction of air under the influence of a temperature change to convert thermal energy into mechanical work.

In a typical implementation, air is repeatedly heated and cooled in a cylinder and the resulting expansion and contraction is used to move a piston and produce useful mechanical work.

Cycle
The Stirling engine uses the temperature difference between its hot end and cold end to establish a cycle of a fixed mass of gas expanding and contracting within the engine, thus converting thermal energy into mechanical power. The greater the temperature difference between the hot and cold sources, the greater the potential Carnot cycle efficiency.

JA 1029 ~ Hot Air Stirling Engine

Engine is fired by denatured alcohol burner . Heat is applied to the end of the glass cylinder . The cylinder is air-tight. Therefore air in the cylinder is permanently sealed inside the engine. This fixed amount of the air is heated & cooled , causing it to expand & contract , this driving the piston.

As the displacer moves up , the air in the cylinder moves down to the hot side , so the air pressure inside the cylinder increase , pushing up on the piston .

As the displacer move down , the air in the cylinder moves up to the cool side , so the pressure inside the cylinder decrease, pulling down on the piston.